Device and method for calibrating linear velocity and track pitch for optical disc

ABSTRACT

A device and method for calibrating linear velocity and track pitch for an optical disc is disclosed. The device comprises a frequency divider, a synchronous bit-clock generator, a counter and a linear velocity and track pitch calculator. The frequency divider receives a motor frequency generator (FG) pulse and generates a motor rotation period signal (FG/X). The synchronous bit-clock generator generates a high frequency bit-clock according to a reproduced signal read from disc. The bit counter counts the pulse of the bit-clock for each period of the motor rotation period signal to generate the data amount M. The linear velocity and track pitch calculator calculates the linear velocity by a linear velocity function with the information of the data amount M and the motor rotation period. Then, the linear velocity and track pitch calculator calculates the track pitch by a pitch function with the information of the data amount, radius and linear velocity at different tracks.

This application is a Continuation of co-pending application Ser. No.10/073,944, filed on Feb. 14, 2002, and for which priority is claimedunder 35 U.S.C. § 120; and this application claims priority ofApplication No. 090103682 filed in Taiwan, R.O.C. on Feb. 16, 2001 under35 U.S.C. § 119; the entire contents of all are hereby incorporated byreference.

BACKGROUND OF THE PRESENT INVENTION

A. Field of the Present Invention

The present invention relates to a device and method for calibrating alinear velocity and a track pitch for an optical disc drive.

B. Description of the Related Art

Optical recording media, such as CD-Rs, CD-RWs, CD-ROMs, DVDs, DVD-RAMs,are usually read by optical disc drives. These optical disc drivescorrectly control the rotation speed of the spindle motor according to areproduced sync signal or a motor frequency generator pulse signal. Inaddition, a precise calculation has to be performed using a“time-to-track” transformation mechanism, so that the laser beam can beshifted to a correct position of the disc (i.e., track jumping). Themechanism of “time-to-track” has to use the parameters of the linearvelocity and the track pitch as a calculation basis. According to thecurrent CD standard, the recording linear velocity must be between 1.2and 1.4 m/s, while the track pitch must be between 1.5 and 1.7 μm.However, the writing speed and track pitch during actual disc playingcannot be predicted. As a result, a slowest writing speed and a maximumtrack pitch are used as the initial calculation basis in the prior art.Then, the values of the linear velocity and the track pitch aresequentially modified according to the relationship between the tracknumber, which is actually fed back during the track jumping, and thetime. However, the laser beam cannot be correctly and quickly shifted tothe correct track in this method, thereby wasting a long period ofseeking time.

To solve this problem, a method for calibrating an optical disc drive,which controls the spindle motor with a constant linear velocity(hereinafter referred to as CLV), has been disclosed. This method,however, cannot calibrate an optical disc drive, which controls thespindle motor with a constant angular velocity (hereinafter referred toas CAV). The prior art method calculates the linear velocity accordingto the ratio of the frame-synchronous signal and disk rotation period.In addition, the prior art method can only calibrate the linear velocitywith respect to optical discs having data recorded thereon, but not theblank discs.

The linear velocity is an important index for measuring the data amountand is helpful to positioning the laser beam precisely. It is thereforean urgent to-be-solved problem as to how to effectively calibrate thelinear velocity and how to apply the calibration method to both the CLVmode and the CAV mode, and to the blank discs.

SUMMARY OF THE PRESENT INVENTION

It is therefore an object of the present invention to provide a methodfor calibrating a linear velocity and a track pitch for an optical discdrive. The method can provide a high-precision calibration regardless ofthe type of the disc, which may be a blank disc or a recorded disc.

Another object of the present invention is to provide a calibrationmethod applicable to any control mode of the spindle motor. Thecalibration method can provide a high-precision calibration on both theCLV and CAV control modes.

To achieve the above-mentioned objects, the present invention provides acalibration device for calibrating linear velocity and track pitch foran optical disc drive. The device includes a bit-clock generator, acounter, and a calculator. The bit-clock generator generates a bit-clocksignal having a frequency higher than that of a reproduced signalaccording to the reproduced signal read from an optical recordingmedium. The counter counts the clocks of the bit-clock generating unitto generate a data amount during a motor frequency generator pulse. Thecalculator calculates the linear velocity and the track pitch of theoptical recording medium according to the data amount and the motorfrequency generator pulse.

The present invention further provides a method for calibration linearvelocity and track pitch for an optical disc drive. The method includesthe following steps. First, the optical disc drive is initialized. Then,the type of the optical recording medium is determined to be a blankdisc or a recorded disc. Next, the laser beam is moved to the lead-inarea. Then, compare the frequency generator pulse of the motor with thereproduced signal of the optical recording medium, so as to calculate afirst data amount. Next, calculate the linear velocity of the opticalrecording medium according to the first data amount and a calibrationequation. Then, move the pick-up to jump any K tracks and calculate thenumber of data blocks passed. Calculate a second data amount. Next,calculate the track pitch according to the linear velocity of theoptical recording medium, the first and second data amount, and atrack-jumping equation.

Further scope of the applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and advantages of the present invention willbecome apparent by reference to the following description andaccompanying drawings, which are given by way of illustration only, andthus are not limitative of the present invention, and wherein:

FIG. 1 is a functional block diagram showing the linear velocitycalibration circuit of the present invention;

FIG. 2 is a synchronous bit-clock generator of the present inventionunder a CAV mode;

FIG. 3 is a synchronous bit-clock generator of the present inventionunder a CLV mode; and

FIGS. 4A to 4B are flow charts showing the calibration steps of thepresent invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

Two signals are used to compute the linear velocity in the presentinvention. The first signal is a frequency generator pulse (hereinafterreferred to as a FG pulse), which is generated when the spindle motor inthe optical disc drive rotates. The second signal is a playback signalor a reproduced signal, (e.g., an EFM (eight-bit to fourteen-bitmodulation) signal or a wobble signal) read from an optical recordingmedium.

FIG. 1 is a block diagram showing a device for calibrating the linearvelocity and track pitch of the present invention. As shown in the FIG.1, a calibration device 10 includes a frequency divider 11, asynchronous bit-clock generator 12, a counter 13, a linear velocity andtrack pitch calculator 14.

The optical disc drive utilizes a motor speed controller (not shown) tocontrol the rotation speed of the optical recording medium. The motorspeed controller generates the FG pulses, for example 6 pulses perrotation of the spindle motor. The frequency of the FG pulses is definedas “Y”. The system can calculate the number of revolutions or the valuesof the rotation angles by using the FG pulses, and control the motorspeed in constant angular velocity. The frequency divider 11 generates arotation period signal (FG/X) corresponding to the rotation speed of theoptical recording medium according to the FG pulses and a setting value(X). If both the Y and X are 6, it means that the calculator of thecalibration device 10 is one revolution of the spindle motor. That is,after the optical recording medium rotates a revolution, the frequencydivider 11 generates a pulse as the rotation period signal.

Reproduced signals can be read from the optical recording medium withdata recorded thereon. For example, the EFM signals may be read from therecording medium, which has been recorded data. The ATIP or wobblesignals can be read from the recording medium without data recordedthereon. The synchronous bit-clock generator 12 generates ahigh-frequency bit-clock BC according to the reproduced signal. Thesynchronous bit-clock generator 12 is a phase-locked loop (PLL) circuit,and generates a bit-clock with an N-time frequency according to theinput signal. At the same time, when the synchronous bit-clock generator12 reaches a locked state, it will output a PLL-locked indicationsignal. The synchronous bit-clock generator 12 has differentarchitectures under the CLV and CAV control states, and the details ofthe architectures will be described in the following.

After the synchronous bit-clock generator 12 outputs a PLL-lockedindication signal, the counter 13 counts the pulse number of thebit-clock BC according to the rotation period signal, and generates adata amount. The counter 13 is for counting the pulse number of thebit-clock BC. Thereby, how many the data amount of the optical recordingmedium is recorded between two rotation period signals can bedetermined. The counter 13 may also output the data amount to thecalculator 14.

The calculator 14 is used to calculate the linear velocity and the trackpitch. The calculator 14 calculates the linear velocity β according toEquation (1): $\begin{matrix}{{\frac{X}{Y} \times \frac{2 \cdot \pi \cdot R}{\beta} \times C} = M} & (1)\end{matrix}$

-   -   wherein X/Y represents the number of revolutions of the optical        recording medium, M represents the data amount outputted from        the counter 13, i.e., the data amount per revolution of the        rotation period signal (FG/X), C represents the output data        amount of the optical recording medium per unit time, and R        represents the position or the radius of the pick-up located on        the optical recording medium. According to the specification of        the optical recording medium, the radius R from the center of        the physical disc to the location of the lead-in 0:2:0 (0th        minute, 2nd second and 0th block) is 25 mm. Therefore, R can be        regarded as a known parameter when calculating M at the location        of 0:2:0. Since X, Y, R, C, and M are known, the linear velocity        β having the unit of m/s can be calculated.

When Equation (1) is used to calculate the linear velocity, differentreproduced signals will be provided different values of C. For instance,if the reproduced signal is the EFM signals and the calculation pulse isthe bit-clock, C is 75*98*588, and M represents the bit amount containedin each FG/X pulse. According a general specification, 75 data blockscan be recorded on the optical recording medium, each data blockcontains 98 EFM frames, each of EFM frame contains 588T (data bitclocks). As can be known form the above-mentioned information, there are75*98*588 bit-clocks contained in a period of time when the opticalrecording medium rotates for one second.

Taking the CD-R or CD-RW for an example, if the calculation pulse is awobble signal, C is 22050, and M represents the wobble-clock amountcontained in each period of the FG/X pulse. If the calculation pulse isa biphase clock, C is 6300, and M represents the biphase clock amountcontained in each period of the FG/X pulses.

Because X, Y, R, C, and M are all known parameters, the linear velocityβ can be surely obtained. At the same time, because the frequency of thebit-clock BC is high, the precision of the linear velocity β iscorrespondingly high. As for the wobble signal or the bi-phase clock,since the resolution thereof is poor, the frequency of the signal,wobble signal or the bi-phase clock, can be multiplied to reach theresolution of the bit-clock BC. For example, the frequency of the wobblesignal can be multiplied by 196, and the frequency of the bi-phase clockcan be multiplied by 686. As a result, the obtained precision of thelinear velocity β can be the same as that of the bit-clock BC.

After the value of the linear velocity β is obtained, the track pitch βcan be further calculated. The present invention derives Equation (2) tocalculate the track pitch t: $\begin{matrix}{{\frac{n}{75} \times \beta} = {{2 \cdot \pi \cdot \left( \frac{R_{1} + R_{2}}{2} \right)} \times \left( \frac{R_{1} - R_{2}}{t} \right)}} & (2)\end{matrix}$

-   -   wherein n represents the total data blocks that have been        jumped, and 75 represents the data blocks passed within one        second. The n/75 represents the elapsed time from the location        of 0:2:0 (0th minute, 2nd second and 0th block) to another        location jumped by n data blocks. The n/75*p represents the        spiral distance there between.

In Equation (2), R₁=25 mm is known, and the data amount M₁ and M₂ can beobtained from the calculator 14, but the value of R₂ is unknown.Fortunately, the linear proportion relationship between M and R can bederived from Equation (1). Therefore, $\begin{matrix}{{\frac{R_{1}}{R_{2}} = \frac{M_{1}}{M_{2}}},{\left. \Rightarrow R_{2} \right. = {\frac{M_{2}}{M_{1}} \times {R_{1}.}}}} & (3)\end{matrix}$

The value of the track pitch t can be obtained from Equations (2) and(3) as follows: $\begin{matrix}{t = {\frac{75\pi}{n\quad\beta} \cdot \left( {\left( \frac{M_{2}}{M_{1}} \right)^{2} - 1} \right) \cdot {R_{1}^{2}.}}} & (4)\end{matrix}$

As can be understood from the description mentioned above, it ispossible for the architecture of FIG. 1 to use a high-precisionbit-clock as a basis for calculating the linear velocity, so theresolution of the calculated track pitch is better. The reading of thereproduced signal of the present invention is not limited to the usageof the EFM sync signal, the wobble signal also can be used to instead.As a result, the calibration result with high precision may be obtainedeven for a blank optical recording medium. Moreover, the linear velocitycalibration of the present invention is also applicable to both the CLVmode and the CAV mode.

FIG. 2 shows an embodiment of the synchronous bit-clock generator thatis applied to the CAV mode. The rotation speed of the spindle motor isconstant in the CAV mode. However, the tangential velocities atdifferent radii of the optical recording medium are different. That is,the feature pattern frequency of the reproduced signal changes with thechange of the radius. The feature extractor 21 reads the reproducedsignals (e.g., EFM or ATIP signals) from the optical recording medium,determines the type of the optical recording medium, and extracts thefeature pattern thereof, such as sync signals, as the reference signalsinputted to the phase-locked loop (PLL) circuit 22. For example, thefeature pattern of the reproduced signal of the optical recording mediumwith data recorded thereon is the EFM sync signal, while the featurepattern of the reproduced signal of the blank optical recording mediumis the ATIP sync signal, bi-phase clock or wobble clock.

The PLL circuit 22 includes an N divider 221, a phase frequency detector222, a loop filter and voltage controlled oscillator 223. Since thefunction and the architecture of the PLL circuit 22 are the same asthose in a general PLL circuit, the detailed descriptions are omitted.The bit-clock generator 12 traces the frequency change of the featurepattern owing to the radius change of the location of the pick-up togenerate the bit-clock signal by using the PLL circuit 22. In addition,since the PLL circuit 22 includes an N divider 221, where N can be setas 588 when taking the EFM as an example, so as to generate a bit-clocksignal having the same frequency as that of the data bit of therecording medium.

FIG. 3 shows an embodiment of the synchronous bit-clock generatorapplied to the CLV mode. The rotation speed of the spindle motor is notconstant in the CLV mode. However, the tangential velocities atdifferent radii of the optical recording medium are the same. Thedifference between FIGS. 3 and 2 resides in that the embodiment of FIG.3 sets the reference signal (bit-clock) to be one with a constantfrequency, obtains the desired linear velocity by controlling therotation speed of the motor, and generates a reproduced feature patterncapable of locking the reference signal. In the embodiment of FIG. 2,however, the rotation speed of the motor is regarded as a constantvalue.

As shown in FIG. 3, a frequency divider 311 divides the frequency of theconstant bit-clock by N. A phase frequency detector 315 and a loopfilter 316 receive the output signals from the frequency divider 311 anda feature extractor 314, and generate the control signals for a controlunit 312. The control unit 312 controls the rotation speed of thespindle motor of the disc drive according to the control signals, so asto keep the same linear velocity for the disc placed thereon. The RFsignal generator 313 is used to read the reproduced signal of the disc.The feature extractor 314 extracts the feature pattern of the reproducedsignal as the feedback signal for the PLL circuit, and determines thetype of the reproduced signal on the optical recording medium. Thefunction and method are the same as those in the embodiment of FIG. 2.

Compared to the functional block diagram of FIG. 1, if the embodiment ofFIG. 2 is adopted by the synchronous bit-clock generator 12, it meansthat the frequency of the FG pulse is a constant value. On the contrary,if the embodiment of FIG. 3 is adopted, it means that the frequency ofthe FG pulse changes under the control of the motor speed controller 312in the synchronous bit-clock generator 12. In fact, FIGS. 2 and 3 havethe similar design rules in which the FG pulse of the motor and thereproduced signal are adopted.

According to the descriptions mentioned above, the flow chart of themethod of calibrating the linear velocity and track pitch of the presentinvention is shown in FIG. 4. From the calculations mentioned above, thecalibrated linear velocity β and track pitch t can be obtained.

Steps 401 to 404 are generalized initial processes. First, at step 401,the optical pick-up (OPU) is moved to the lead-in area. Then, at step402, the laser beam is activated to focus so as to read the RF signalthat is reflected back from the optical recording medium. Next, at step403, the motor is controlled to be the CLV mode or the CAV mode. Then,at step 404, the operations of track-locking and reading are performedso as to align the track and read the RF reproduced signal.

At step 405, it is judged that whether the optical recording mediumcontains data according to whether an EFM signal is contained in the RFreproduced signal. If the optical recording medium is a blank medium,the ATIP signal is used as a basis for calibrating the signal.Otherwise, the EFM signal is used as a basis for calibrating the signal.Then, at step 406, the optical recording medium is configured to locateat 0:2:0, the initial position of the data record. That is, the opticalrecording medium is configured to locate at a position of radius of 25mm (R₁) of the optical recording medium.

Then, the calculator in FIG. 1 is activated to compare the frequencygenerator pulse of the motor with the reproduced signal of the opticalrecording medium, so as to obtain the value of the first data amount M₁.Next, at the step 407, the linear velocity β of the optical recordingmedium are calculated according to the first data amount M₁ and theabove-mentioned equations for calculating the linear velocity.

Then, at step 408, the OPU is moved by any K tracks to the location of aradius of R₂ to measure the time code for reaching the location and tocalculate the data blocks n or block number passed by the jumping of Ktracks. Next, at step 409, the calculator is again activated to comparethe frequency generator pulse of the motor with the reproduced signal ofthe optical recording medium, so as to calculate the value of the seconddata amount M₂.

After the values of M₁, M₂, and the linear velocity β is obtained, thevalue of track pitch t can be obtained from the above-mentionedtrack-jumping equation (4), so as to precisely get the track pitch.Finally, at step 411, the calibration processes are ended.

To sum up, the present invention is applicable to high-precisioncalibrations under any constant rotation speed regardless of theconfiguration of the optical disc drive is a CLV mode or a CAV mode.Furthermore, since the present invention uses the bit-clock signal as ameasurement unit, the calibration result can be more precise incomparison with the prior art using the EFM sync signal. Moreover, thepresent invention can use the ATIP signal as a basis for calibration,the linear velocity calibration also can be performed even though nodata is recorded on the optical recording medium.

While certain exemplary embodiments have been described and shown in theaccompanying drawings, it is to be understood that such embodiments aremerely illustrative of and not restrictive on the broad invention, andthat this invention not be limited to the specific constructions andarrangements shown and described, since various other modifications mayoccur to those ordinarily skilled in the art.

1. A calibration device for calibrating a linear velocity and a trackpitch for an optical disc drive, comprising: a bit-clock generator forgenerating a bit-clock signal having a frequency higher than that of areproduced signal according to the reproduced signal read from anoptical recording medium; a data amount counting unit for counting thepulses of the bit-clock signal for each motor frequency generator pulseto generate a data amount; and a calculator for calculating the linearvelocity and the track pitch of the optical recording medium accordingto the data amount and the motor frequency generator pulse.
 2. Thecalibration device according to claim 1, further comprising a frequencydivider for receiving an output pulse from a spindle motor to generatethe motor frequency generator pulse according to a setting value.
 3. Thecalibration device according to claim 1, wherein the data amountcounting unit is a counter.
 4. The calibration device according to claim1, wherein the bit-clock generator comprises: a feature extractor fordetermining the type of the optical recording medium according to thereproduced signal, and outputting a reference signal; and a phase-lockedloop circuit for outputting the bit-clock signal according to thereference signal.
 5. The calibration device according to claim 2,wherein the bit-clock generator comprises: a feature extractor fordetermining the type of the optical recording medium according to thereproduced signal, and outputting a feedback signal; a phase-locked loopcircuit for receiving the feedback signal from the feature extractor anda constant-frequency pulse, and generating a control signal; a controlunit for controlling the rotation speeds of the spindle motor and thedisc according to the control signal from the phase-locked loop circuit;and an RF signal generator for generating the reproduced signal of thedisc.
 6. The calibration device according to claim 4, wherein thereproduced signal is an EFM sync signal, an ATIP signal or a wobblesignal.
 7. The calibration device according to claim 5, wherein thereproduced signal is an EFM sync signal, an ATIP signal or a wobblesignal.
 8. The calibration device according to claim 2, wherein thecalculator calculates the linear velocity β according to the followingequation:${{\frac{X}{Y} \times \frac{2 \cdot \pi \cdot R}{\beta} \times C} = M},$wherein Y represents the pulse number per revolution of the spindlemotor, X is a frequency divisor of the motor frequency generator pulse,M is the data amount measured from the counter, R represents the radiusof the position where an optical pick-up located on the opticalrecording medium, and C represents a bit-clock amount contained in theoptical recording medium per unit time.
 9. The calibration deviceaccording to claim 8, wherein the position of the radius R is a positionof 0th minute, 2nd second and 0th block, and R=25 mm.
 10. Thecalibration device according to claim 8, wherein the calculatorcalculates the track pitch t according to the following eqution:${t = {\frac{75\pi}{n\quad\beta} \cdot \left( {\left( \frac{M_{2}}{M_{1}} \right)^{2} - 1} \right) \cdot R_{1}^{2}}},$wherein n represents the number of data blocks passed after any K tracksare jumped, 75 represents the number of data blocks contained in onesecond, R₁ represents a first radius of the optical pick-up, M₁represents a first data amount, and M₂ represents a second data amount.11. The calibration device according to claim 10, wherein the positionof the radius R is a position of 0th minute, 2nd second and 0th block,and R=25 mm.
 12. A method for calibration a linear velocity and a trackpitch for an optical disc drive, comprising the steps of: initializingthe optical disc drive; determining the type of the optical recordingmedium; moving a pick-up to a lead-in area; comparing a frequencygenerator pulse of the motor with a reproduced signal of the opticalrecording medium so as to get a value of a first data amount;calculating the linear velocity of the optical recording mediumaccording to the value of the first data amount and a calculationequation; calculating the number of data blocks passed after any tracksare jumped, and getting a value of a second data amount of the tracks;and calculating the track pitch t according to the linear velocity ofthe optical recording medium, the value of the second data amount, and atrack-jumping equation.
 13. The method according to claim 12, whereinthe step of initializing the optical disc drive comprises the followingsteps of: moving the pick-up to the lead-in area; activating a laserbeam and focusing the laser beam; setting a rotation control mode forthe motor; and positioning a track and reading the reproduced signal onthe disc.
 14. The method according to claim 12, wherein the equation forcalculating the linear velocity β is:${{\frac{X}{Y} \times \frac{2 \cdot \pi \cdot R}{\beta} \times C} = M},$wherein Y represents the pulse number generated after the motor rotatesa revolution, X is a frequency divisor of the motor frequency generatorpulse, M is a value of the data amount, R represents the radius of theposition where an optical pick-up located on the optical recordingmedium, and C represents a bit-clock amount contained in the opticalrecording medium per unit time.
 15. The method according to claim 12,wherein the equation for calculating the track pitch is:${t = {\frac{75\pi}{n\quad\beta} \cdot \left( {\left( \frac{M_{2}}{M_{1}} \right)^{2} - 1} \right) \cdot R_{1}^{2}}},$wherein n represents the number of data blocks that are jumped, 75represents the number of data blocks contained in one second, R₁represents a first radius of the position of the pick-up when thepick-up starts, M₁ represents a first calculated data amount, and M₂represents a second calculated data amount.
 16. The method according toclaim 15, wherein the position of the radius R is a position of 0thminute, 2nd second and 0th block, and R=25 mm.
 17. The method accordingto claim 12, wherein the reproduced signal includes an EFM sync signal,an ATIP signal or a wobble signal.